We tested the hypothesis that continued secretion of gonadal steroids is necessary to suppress hibernation in male golden-mantled ground squirrels in the weeks after the terminal arousal in spring. Juvenile and adult males were gonadectomized or sham gonadectomized 1 wk after the terminal arousal; 64% of castrated and none of the shamcastrated animals resumed hibernation. Latency to resumption of torpor was 9 +/- 2 days from the time of castration, and squirrels underwent 4.3 +/- 0.9 bouts before permanently regaining euthermia. Among squirrels that resumed hibernation, bout duration was significantly shorter and torpor was shallower after castration. Castration as late as 3 wk after the terminal arousal reinstated hibernation. We suggest that the terminal arousal of male squirrels in the spring is provoked by a steroid-independent mechanism similar to that operating earlier in the hibernation season; abandonment of hibernation is contingent on concomitant sustained increases in androgen secretion during the first few weeks of euthermia.